1. Field of the Invention
The present invention is related to a step-up power supply circuit for producing a higher step-up voltage than a preselected power supply voltage, and also to a semiconductor integrated circuit device equipped with the step-up power supply circuit.
2.
Conventionally, in an electronic appliance with employment of a dry cell and an on-vehicle battery, having relatively low output voltages, a step-up power supply circuit is provided. The step-up power supply circuit produces a step-up voltage in response to the output voltage of the above-described power supply. This step-up voltage is used as an operating power supply voltage in this electronic appliance.
FIG. 11 represents an example of an electronic appliance arranged by employing the above-described conventional step-up power supply circuit 1 and a semiconductor integrated circuit device 2 having a plurality of amplifiers AM.sub.0 to AM.sub.3. In this drawing, the step-up power supply circuit 1 is equipped with a rectangular wave generating circuit 4 and a step-up circuit 5, which are operated under a power supply voltage Vcc outputted from a power supply 3 such as a dry cell and an on-vehicle battery.
The rectangular wave generating circuit 4 is constituted by an astable multivibrator and the like, which outputs such a rectangular wave Sc. The amplitude of this rectangular wave is rapidly inverted in a predetermined time period. The step-up circuit 5 is arranged by a voltage doubler rectifying circuit equipped with a rectifying diode and a capacitor. The step-up circuit 5 ON/OFF-controls the rectifying diode in synchronism with the rectangular wave Sc to charge the capacitor, so that a step-up voltage HVcc higher than the power supply voltage Vcc is produced.
This step-up voltage HVcc is applied to the semiconductor integrated circuit device 2, and since the amplifiers AM.sub.0 to AM.sub.3 are operated while using the step-up voltage HVcc as the operating power supply voltage, these amplifiers AM.sub.0 to AM.sub.3 amplify signals entered into input terminals IN.sub.0 to IN.sub.3 to thereby output the amplified signals to the respective output terminals Q.sub.0 to Q.sub.3.
On the other hand, in the above-described conventional step-up power supply circuit 1, since the rectifying diode contained in the step-up circuit 5 is ON/OFF-controlled based upon the rectangular wave Sc containing the radio frequency (high frequency) components, the RF (radio frequency) switching noise is produced from the rectifying diode. There is a problem that this RF switching noise is entered into the amplifiers AM.sub.0 to AM.sub.3 provided in the semiconductor integrated circuit device 2 and then is mixed with the respective amplified signals derived from the output terminals Q.sub.0 to Q.sub.3.
Also, there is another problem that in order to prevent adverse influences caused by the switching noise, a total number of externally provided components such as the noise absorbing capacitors, resistors, or coils is increased.
Also, in order to avoid the above-explained adverse influence caused by the switching noise given to the semiconductor integrated circuit device 2, since the step-up power supply circuit 1 and the semiconductor integrated circuit device 2 are separately arranged from each other, a total number of electronic component would be increased. Furthermore, it is practically difficult to realize a high-performance electronic appliance within a limited volume in a high density. Also, it is practically difficult to realize such a semiconductor integrated circuit device containing the conventional step-up power supply circuit 1, and also the amplifiers AM.sub.0 to AM.sub.3 which are susceptible to the noise adverse influence.
When the step-up voltage HVcc produced by the step-up circuit 5 is used as the operating power supply voltage to drive the amplifiers AM.sub.0 to AM.sub.3, there is such an effect that the dynamic range can be improved. However, in order to actually achieve this effect, the amplification factors of the amplifiers AM.sub.0 to AM.sub.3 is required to be increased in response to the increase in the stepped-up operating power supply voltage.
That is to say, in such a case that both the amplitudes of the input signals entered into the amplifiers AM.sub.0 to AM.sub.3, and the amplification factors of the amplifiers AM.sub.0 to AM.sub.3 are the same as those of each other irrespective to high/low operating power supply voltages of the amplifiers AM.sub.0 to AM.sub.3, the output signals outputted from the amplifiers AM.sub.0 to AM.sub.3 are equal to each other irrespective of the high/low operating power supply voltages. As a result, in order to actually achieve the effect of the wide dynamic range, the amplification factors of the amplifiers AM.sub.0 to AM.sub.3 are required to be increased in response to increasing of the operating power supply voltage.
However, conventionally, while the variable resistors and the like are connected to the amplification factor adjusting terminals provided with the amplifiers AM.sub.0 to AM.sub.3, the amplification factors are adjusted by manually adjusting the values of the variable resistors. As a result, there are problems that the adjusting work becomes cumbersome, and furthermore, the externally provided electronic components such as the above-explained variable resistors are required, which induces an increase of total numbers of such electronic components.